Synthesis And Luminescent Properties Of Ions-Doped SrLaGa₃O₇ Phosphors With Disordered Crystal Structure

The ABC₃O₇（A=Ca,Sr,Ba;B=rare-earth ions;C=Ga,Al）typed crystal is a disordered structure consisting of C_ⅠO₄^5-and C_ⅠⅠO₄^5-type tetrahedra through a co-vertex pattern.The disorderly arrangement of the A and B ions makes the structure between conventional crystals and glasses,and thus combines the disorderly nature of glasses and the ordered nature of crystals.In terms of performance,it has the advantage of non-uniform broadening spectrum of glass.Meanwhile,its thermal conductivity increases with the increase of temperature due to the characteristics of both centerless and non-centered structures,and thus has good heat dissipation ability.In this work,a series of Sr La Ga₃O₇-based phosphors were prepared by selecting Sr La Ga₃O₇matrix materials doped with Bi³⁺,Mn⁴⁺,Tb³⁺,and Eu³⁺ions,resolving their structures and studying their fluorescence properties,and initially exploring the correlation between disorder and optical properties in ion-doped melilite structure ABC₃O₇-type fluorescent materials.The main researches are as follows:（1）The physical and optical properties of Bi³⁺-doped SrLaGa₃O₇-based phosphors were speculated using the first-principle calculations.Firstly,the forbidden band width of the doped phosphors and the densities of states distribution of the electron orbitals of different elements were researched.Secondly,the possible optical properties were speculated based on the densities of states distribution.The theoretical calculations are also verified based on the experimental results of Bi³⁺-doped Sr La Ga₃O₇-based phosphors.（2）The physical phase,crystal structure and fluorescence properties of Mn⁴⁺and Bi³⁺/Mn⁴⁺-doped Sr La Ga₃O₇-based phosphors were systematically investigated.The occupancy of the doped ions in the Sr La Ga₃O₇matrix was determined based on the ionic radius theory.The composition of the phosphor’s phase and the binding energy of the elemental electron orbitals were determined based on the X-ray diffraction and X-ray photoelectron spectroscopy results.The optimal excitation wavelength of phosphor was determined based on UV-Vis absorption spectra and photoluminescence excitation spectra.Potential applications of different ion-doped Sr La Ga₃O₇-based phosphors were determined based on photoluminescence spectra.The Bi³⁺-Mn⁴⁺energy transfer in Bi³⁺/Mn⁴⁺co-doped Sr La Ga₃O₇-based phosphors was determined by combining the fluorescence decay test results.Based on this energy transfer,the dopant ion concentration was adjusted to obtain tunable fluorescent performance Bi³⁺/Mn⁴⁺co-doped Sr La Ga₃O₇-based phosphors.（3）The phases,crystal structures and fluorescence properties of Eu³⁺,Tb³⁺and Bi³⁺/Eu³⁺/Tb³⁺-doped Sr La Ga₃O₇-based phosphors were systematically investigated.The energy transfer process of Bi³⁺-Eu³⁺,Bi³⁺-Tb³⁺,Tb³⁺-Eu³⁺and the tunable fluorescence properties of Bi³⁺/Eu³⁺/Tb³⁺triple-doped SrLaGa₃O₇-based phosphors based on the energy transfer were studied.The prepared Bi³⁺/Eu³⁺/Tb³⁺tri-doped Sr La Ga₃O₇-based phosphors were combined with UV LED chips and assembled to obtain warm white LED devices.（4）The upconversion and downconversion fluorescence properties of Er³⁺and Yb³⁺co-doped Sr La Ga₃O₇-based phosphors were systematically investigated,and the upconversion and downconversion fluorescence mechanisms and the effects of different luminescence mechanisms on the fluorescence properties were elaborated by combining the electronic energy levels of Er³⁺and Yb³⁺ions.